Problem: Simplify the following expression: $n = \dfrac{z}{4} - \dfrac{z}{2}$
Explanation: In order to subtract expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $4$ and $2$ $\lcm(4, 2) = 4$ $ n = \dfrac{1}{1} \cdot \dfrac{z}{4} - \dfrac{2}{2} \cdot \dfrac{z}{2} $ $n = \dfrac{z}{4} - \dfrac{2z}{4}$ $n = \dfrac{z -2z}{4}$ $n = \dfrac{-z}{4}$